Antoine Boesset (1586-1643), surintendant de la musique de la chambre to Louis XIII, has long been known as one of the most important composers active in early seventeenth-century France, but until recently he was believed to have produced only secular airs de cour. This edition presents for the first time Boesset¿s newly identified sacred works, a repertory of some seventy compositions for the nuns of the Royal Abbey of Montmartre, Paris. Scored for multiple high voices, bass and basse continue, Boesset¿s works include three complete mass ordinary settings (through composed and alternatim), Te Deums and Magnificats (again both through composed and altneratim), psalms, and a number motets for important feasts and ceremonies at Montmartre. Montmartre was also one of the first religious houses to adopt so-called ¿plain chant musical,¿ a type of newly composed or modified chant. Several works of the edition make particular use of this kind of chant, most notably the alternatim hymn settings, which use unusual metered versions of the newly composed hymn chants in alternation with the polyphony. Boesset¿s compositions for Montmartre represent by far the largest single repertory of sacred music from the reign of Louis XIII, and, while not showing the influence of the newest Italian practices, nevertheless anticipate several of the musical techniques previously associated with Henri Dumont, in particular the use of the basse continue. These works thus fill a significant gap in our understanding of musical developments in seventeenth-century France and demonstrate that sacred music of the highest quality emerged during a period that scholars have long dismissed as being of little interest.